This is a new creation of mine. The purpose of this antenna is to load up 40m on a compact, light-weight, easily packed antenna using materials I have on hand.
The main support for the vertical is a 16.5′ long Black Widow Crappie pole. I got it from Cabelas for <$15 several months ago. It makes a nice wire antenna support for /PM as well as portable. Th coil is a scrap length of some #10 or so aluminum grounding wire from Radio Shack. It is no specific length. The coil is 16 turns, 3.5"d, and the coil spacing is 5/8". There is no rhyme or reason behind the dimensions - that’s just what I threw together HI. As you can see, its a bit on the rough side. The top and bottom (the brown discs) are cut from coffee can lids. I cut the center hole exactly to the dimensions of the crappie pole section. The top disc rests on the top of the third section and the bottom disc is snug against the third section. It fits like a glove! (the coffee can lids are soft plastic – you can cut them undersize and they will stretch a bit over the pole). The discs are attached with hot glue (as you can tell). I cut holes in the discs where they touched the coil spacers so that I could get glue all the way through the plastic. I didn’t want the glue to come loose from the plastic (it won’t stick to it too well), the glue passing all the way through kind of acts like a pin.
Here is the coil tapped for 30m. I can’t get 40m on this coil, the lowest frequency I can get on is 9.600MHz.
I made another coil out of a Slinky. One of the end caps I made broke off so Im not using it at the moment. This one will get me on 40m, but the coil is pretty cumbersome. The form for this coil is the backing to some 2×3′ paper. I rolled it up tightly and then slipped the slinky over top. When I let go of the cardboard it sprang open to fit the inside of the slinky. The turns can still be moved around, but they aren’t loose.
Here is a close up of the base I am using. It is made from 1-1/2″ PVC tube. There is a 1/2″ metal rod bolted to the back side. In the second image you can see the nutts holding it on. I glued two 3/4″ 10-24 bolts in the metal rod. The position of the bolts allow the rod to be unbolted and stuck back up inside the tube for transport. The SO-239 on the front has a pigtail attached for connecting the radiator. I used Anderson Power Pole connectors for a quick disconnect. They work pretty well, and as with everything else in this antenna I had them in the junk box.
Like I said, I made this antenna to load up on 40 meters. I know I can get 20-10 without the coil just by adjusting the length of the wire. I fold the wire over and wrap it around itself to load the higher bands (given I use a bare top wire). It works pretty well. It takes a little while to get the tuning correct, but I can do it. This way I don’t need to lug a tuner around with me – I have a “resonant” antenna (more or less, it is probably not completely efficient, though I do loose the attenuation in the tuner and coax). The antenna just isn’t long enough to get me on 30 or 40 meters without the coil.
I will work on some other coils as I have time and see if I can get this antenna perfected. I might try to get on 80 too. It will take a large coil but I might be able to do it. I also might start experimenting with a capacitace hat. That might be all I need to get my current good coil to load 40. I won’t know until I try!
I just finnished up a new coil. This one is 26 turns, 7 turns/inch, 4.625″d. I calculated the inductance using an equation I found on AD5X’s website – 53.9uh! My other coil (the silver one, not the slinky) showed 10.8uh when I measured it with an inductance meter. I think Ill be able to get 40m on this one HIHI. Maybe 80m too?
The coil on the right is the new one, the one on the left is the old one
I am working on some radials too. I found a scrap of some phone (I think) cable in a bag I stuffed in the crawl space a couple years ago. It is 25 pairs (50 strands total) and just happens to be right about 1/4w on 40. I stripped it and pulled out all the strands. I am not sure how well they will work because of them being so tiny, but 50 of these ought to be enough for a decent ground I would think. Now I just need to figure out how to connect them to the antenna. Maybe a loop on one end and a few bolts on the base? If I do 2 bolts thats 25 wires on each one. If I clamp down on them fairly tight I might be able to get a decent connection.
If I get a chance here in the next couple days Ill test this one out. I am pretty confident it is going to work, I have done a lot of studying up on these after my failed attempt at winging it on the old one (no calculations or anything, I just spun out a coil with what I had on hand HI – no surprise it didn’t work well). The weather is suppoesd to be pretty crappy, I don’t know if I will get the chance to test this or not.
The new coil works GREAT! I just had the antenna set up and it works real well. The antenna resonates at 13 turns (out of 26). I can get 40 and 20 meters at the same time without changing the tap – flat on 20 and not quite 1:1 on 40, around 1.2:1 or so (which is where it should be I do believe – its a vertical and the characteristic impedance of a vert is less than 50 ohms, so if its 1.2:1 that means the impedance is around 40 ohms).
I was using 4 – 1/4wl radials (on 40m, about 32-34′). I have 5 to toss on there now, I was just lazy and didn’t feel like adding the extra 5th HI.
The phone cable is still in the works. I might just break it in to the 25 pairs instead of tear those apart for 50 strands – thats a LOT of extra work. Or, I might just scrap that and go with the 5 radials I have right now.
The coil won’t quite get me on 80m, but I can get down below 5mHz (which means I can get 60m too).
My next idea is to combine the two coils to see if I can load up 80 on this too HI. That should be quite interesting. I am sure my ERP will REALLY be suffering down there, but it won’t be quite as bad as if I base loaded the antenna.
I am at my Dad’s place for Christmas and brought along the antenna and radio. I have had the antenna up in the back yard for a couple days now. We are getting a LOT of wind. Last night the rod on my mount broke and the antenna fell over. The wind had been throwing the antenna all over the place bending the rod stuck in the ground back and forth. It broke at the bottom hole where the bolt attaches it to the PVC (see the second picture of the mount above). It just got metal fatigue and failed. I pounded some steaks in the ground at the base and lashed the PVC mount inside of them, so it is secure for now. It has been up all day and hasn’t moved as far as I can tell. After the holidays I’ll work on perfecting the mount.
I still haven’t tried adding in the second coil to see if I can load up 80m. I have just been content on 40.
Here are some pictures I just took. This first one is of the rod that broke. You can see how the rod works on the mount in the two pictures up above.
Here is my jimmy-rigged base. I used some wood steaks and about 2′ of 14g solid copper wire as a tie HI. Hey, it worked.
Here is the antenna all put together and running on 40. I put the plastic over it because it has been out for a while in the weather. I didn’t want my coil or the connections down at the base to get wet in the rain. It probably wouldn’t hurt if they got wet a couple times, there is nothing that will soak up water (other than the coax HI) or change impedance (or very little).
I decided to put this choke in the coax to keep the RF off the shield. I also figured the coax could be a radial too. I am not sure how well that theory holds up, though HI.